Type VI collagen is a microfibrillar component found in most soft tissues and in cartilage. The triple-helical molecules are composed of three constituent chains, alpha2(VI), alpha2(VI) and alpha3(VI) chains. Several polymorphic mRNAs encoding for alpha2(VI) and alpha3(VI) variants are transcribed from the genes by alternative splicing mechanism. The long term objectives of this grant are to elucidate the biological function of collagen VI and to investigate whether defects in collagen VI are associated with heritable or acquired connective tissue diseases. The specific aims of this competing continuation application are: (1) To define the biological significance of the variation in mRNAs for the alpha2(VI) and alpha3(VI) chains. The distribution of mRNA and protein variants will be determined in human cell lines and mouse tissues of different developmental stages. (2) To define the molecular requirements for the assembly of the collagen VI triplehelical molecules. The approach will be to express full-length or partial cDNAs of each chain in mammalian cells and to study the assembly of the triple-helices. (3) To define the functional role of specific domains in each of the three collagen VI chains. Fusion proteins containing specific domains and variant domains will be prepared in bacterial or mammalian cells expression vectors and used for functional studies. (4) To examine the complexity of collagen VI structure in tissues by searching for isoforms of collagen VI chains and for associated noncollagenous proteins. (5) To complete the isolation of genomic clones for the alphal(VI), alpha2(VI) and alpha3(VI) collagen genes and to define the important structural features of the genes. (6) To identify cis- and trans-regulatory elements that control the expression of the three collagen VI genes.